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Ligand influences on homoleptic Group 12 m-terphenyl complexes† Toby J. Blundell, Fiona R. Hastings, Benjamin M. Gridley, Graeme J. Moxey,‡ William Lewis, Alexander J. Blake and Deborah L. Kays* Three m-terphenyl ligands 2,6-Ar2C6H3− [Ar = 2,6-Me2C6H3 (2,6-Xyl); 3,5-Me2C6H3 (3,5-Xyl); 2,3,4,5,6Me5C6 (Pmp)] have been used to stabilise three series of two-coordinate Group 12 diaryl complexes; (2,6Ar2C6H3)2M [M = Zn, Cd, Hg, Ar = 2,6-Xyl 1–3, 3,5-Xyl 4–6, Pmp 7–9], where differing steric demands on the metal centres are imparted. These are the first homoleptic d-block complexes featuring any of these
Received 3rd March 2014, Accepted 3rd April 2014
ligands. Complexes 1–9 have been characterised in solution and the solid state; the analysis of structural
DOI: 10.1039/c4dt00647j
changes produced by differences in ligand properties is reported. In particular, complexes 4–6 show smaller C–M–C bond angles and contain secondary ligand interactions that are not seen in the analogous
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complexes 1–3 and 7–9.
1.
Introduction
Since the first report of diethylzinc by Edward Frankland in 1848,1 the investigation of the synthesis and reactivity of organogroup 12 complexes has become an important research area, driven by the use of these compounds in catalysis and materials chemistry. Examples of this include the key role which organozinc reagents play in a range of fundamental organic transformations,2 copolymerisation reactions between carbon dioxide and epoxides to yield polycarbonate compounds,3 alkali-metal mediated zincation reactions,4 cadmium complexes as molecular precursors for photoluminescent quantum dot synthesis5 and mercury compounds as ligand transmetallation reagents.6 The number of two-coordinate Group 12 organometallic complexes in the literature is relatively low, as solid state structures often contain secondary interactions which result in a metal coordination number of greater than two.7,8 Due to this, more sterically demanding ligands have been utilised to stabilise lower coordination numbers, for example in the m-terphenyl complex (2,6-Mes2C6H3)2Hg (Mes = 2,4,6-Me3C6H2).9 The use of sterically demanding m-terphenyl ligands in Group 12
School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD, UK. E-mail: [email protected]; Fax: +44 (0)115 9513555; Tel: +44 (0)115 9513461 † Electronic supplementary information (ESI) available: Crystallographic data for complexes 1–9, molecular structures and crystallographic data for iodides 2,6Ar2C6H3I (Ar = 2,6-Xyl, 3,5-Xyl, Pmp) and [2,6-(3,5-Xyl)2C6H3Li]2. CCDC 989599–989611. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4dt00647j ‡ Current address: Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia.
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chemistry has led to the synthesis and structural characterisation of the first series to feature homologous Group 12 M–M bonds (2,6-Dipp2C6H3)2M2 (M = Zn, Cd, Hg; Dipp = 2,6-iPr2C6H3), the hydride compounds [(2,6-Dipp2C6H3)MH]n (M = Zn, Cd, n = 2; M = Hg, n = 1)10,11 and (η5-C5H5)2Zr (ZnC6H3-2,6-Trip2)2 (Trip = 2,4,6-iPr3C6H2), which contains a Zn–M–Zn (M = transition metal) moiety.12 Our previous investigations have shown that changes in m-terphenyl ligand architectures can result in significant differences in structure, bonding and small molecule reactivity.13–15 We are interested in deducing how subtle changes in the steric pocket offered by the m-terphenyl ligands can affect the coordination environment around the metal centre, with the eventual aim of tailoring the ligand sterics towards the investigation of bonding and small molecule reactivity. To this end we report three series of two-coordinate Group 12 bis-terphenyls of the form (2,6-Ar2C6H3)2M (M = Zn, Cd, Hg; Ar = 2,6-Xyl, 3,5-Xyl, Pmp), which represent the first series of structurally authenticated homoleptic Group 12 bis-terphenyl complexes. Comparison of the crystal structures of these compounds as a function of flanking aryl group illustrates how the manipulation of the steric pocket provided by these ligands influences the structures of the complexes. The general structures of the ligands used in this investigation are shown in Fig. 1.
Fig. 1 The m-terphenyls used in this investigation: R1 = Me, R2 = R3 = H (2,6-Xyl); R1 = R3 = H, R2 = Me (3,5-Xyl); R1 = R2 = R3 = Me (Pmp).
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2. Results and discussion
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2.1.
Synthesis and spectroscopic characterisation
The reaction between the three lithium complexes [2,6Ar2C6H3Li]2 (Ar = 2,6-Xyl; 3,5-Xyl; Pmp)16,17 and ZnCl2, CdCl2 or HgBr2 in a mixture of toluene and THF at room temperature yields the diaryl complexes [2,6-(2,6-Xyl)2C6H3]2M (M = Zn 1, Cd 2, Hg 3), [2,6-(3,5-Xyl)2C6H3]2M (M = Zn 4, Cd 5, Hg 6) and [2,6-Pmp2C6H3]2M (M = Zn 7, Cd 8, Hg 9), respectively, in low to moderate yields according to Scheme 1, although it must be stressed that these are yields of crystalline materials and are not optimised. Crystallisation of 1–6 was achieved by slow cooling to −30 °C of hexane solutions of the complexes. Crystals of 7·0.5C6H14 and 9 were obtained by storage of saturated hexane solutions at room temperature, whereas slow cooling to 6 °C of a saturated hexane solution of 8 proved successful for crystal growth. Complexes 1–9 have been characterised by NMR spectroscopy, elemental analysis and mass spectrometry, and from the results of single crystal X-ray structure determinations. The NMR spectroscopic measurements on 1–9 all indicate one ligand environment in solution. This is in contrast to the NMR spectra recorded for (2,6-Naph2C6H3)2Zn and (2,6Naph2C6H3)2M(OEt2) (M = Cd, Hg; Naph = 1-C10H7), where syn and anti ligand conformations lead to multiple isomers of the complexes in solution.14 The cadmium and mercury NMR spectra for 2, 3, 5, 6, 8 and 9 each shows a single peak (113Cd{1H} range = 393.47 to 466.08 ppm and 199Hg{1H} range = −546.31 to −702.88 ppm) and are in the ranges observed for similar diaryl compounds.14,18 In both the 113Cd{1H} and 199 Hg{1H} NMR spectra of these complexes the chemical shifts follow a broad upfield trend with increasing steric demands on the metals: [2,6-(3,5-Xyl)2C6H3]2M > [2,6-(2,6-Xyl)2C6H3]2M > [2,6-Pmp2C6H3]2M. 2.2.
Crystallographic characterisation
Apart from the solid state structure of 7·0.5C6H14, which crystallised with half a molecule of hexane in the asymmetric unit, there are no solvent molecules present within the crystal structures of these complexes. As a consequence of the steric demands of the m-terphenyl ligands, complexes 1–9 are monomeric in the solid state. The nearest M⋯M separations are d(Zn⋯Zn) = 9.7 Å (for 4), d(Cd⋯Cd) = 10.5 Å (for 2) and d(Hg⋯Hg) = 9.9 Å (for 3). The solid state structures of these compounds feature the metal centres bound to two terphenyl ligands and the metal centres are two-coordinate in all cases. This is in contrast to the Group 12 complexes of the 2,6-
Naph2C6H3− ligand where the cadmium and mercury diaryls are three-coordinate [(2,6-Naph2C6H3)2M(OEt2) (M = Cd, Hg)],14 and is presumably due to the overall lower steric demands of the 1-naphthyl moiety compared to the 2,6-Xyl, 3,5-Xyl or Pmp substituents. Relevant bond lengths and angles for 1–3 can be found in Table 1, for 4–6 in Table 2 and for 7–9 in Table 3. The Zn–C distances for 1 [Zn(1)–C(1) = 1.949(4) Å, Zn(1)– C(23) = 1.944(4) Å], 4 [Zn(1)–C(1) = 1.9362(13) Å, Zn(1)–C(23) = 1.9402(13) Å] and 7 [Zn(1)–C(1) and Zn(1)–C(29) = 1.939(3) Å], are similar to each other and to the values for two-coordinate (2,6-Naph2C6H3)2Zn [Zn–C = 1.946(2) and 1.955(2) Å].14 Cd–C bond lengths for 2, 5 and 8 and Hg–C bond lengths for 3, 6 and 9 also occur in relatively narrow ranges [Cd–C = 2.112(2)– 2.130(2) Å and Hg–C = 2.087(5)–2.102(6) Å] and are similar to those found for other two-coordinate cadmium8,19 and mercury diaryls.9,20 The shorter M–C distance in the mercury diaryls compared to their cadmium analogues is attributed to the smaller covalent radius of mercury compared to cadmium, and is presumably due to a combination of relativistic effects and the lanthanide contraction.10,21 Table 1
Selected bond lengths (Å) and angles (°) for 1–3
C(1)–M(1) C(23)–M(1) C(1)–M(1)–C(23) C(1)plane⋯C(23)plane C(1)plane⋯flanking aryl plane
Table 2
1 (M = Zn)
2 (M = Cd)
3 (M = Hg)
1.949(4) 1.944(4) 178.7(2) 83.6(2) 88.4(2) 80.73(19) 83.0(2) 84.1(2)
2.115(5) 2.228(5) 179.9(3) 84.2(3) 82.2(3) 87.0(3) 84.3(3) 84.8(3)
2.087(6) 2.101(5) 177.1(2) 86.62(18) 83.34(16) 83.65(16) 83.8(2) 87.4(2)
Selected bond lengths (Å) and angles (°) for 4–6
C(1)–M(1) C(23)–M(1) C(1)–M(1)–C(23) C(1)plane⋯C(23)plane C(1)plane⋯flanking aryl plane
4 (M = Zn)
5 (M = Cd)
6 (M = Hg)
1.9362(13) 1.9402(13) 171.18(5) 86.67(4) 56.11(5) 51.26(5) 50.04(5) 40.36(5)
2.119(2) 2.130(2) 174.10(9) 86.63(7) 52.71(9) 56.33(9) 45.00(10) 48.69(10)
2.093(6) 2.102(6) 176.4(2) 86.03(19) 55.6(2) 57.8(2) 49.6(2) 47.1(2)
Table 3 Selected bond lengths (Å) and angles (°) for 7–9. Symmetry operation: ’ = −x + 1/4, −y + 1/4, z
7 (M = Zn) 8 (M = Cd) 9 (M = Hg) C(n) = C(29) C(n) = C(1′) C(n) = C(1′)
Scheme 1 Synthesis of diaryl complexes (2,6-Ar2C6H3)2M (M = Zn, Cd, Hg; Ar = 2,6-Xyl 1–3; 3,5-Xyl 4–6; Pmp 7–9). Reaction conditions: (i) Toluene–THF, −78 °C→RT, 16 h, −2 LiX.
14258 | Dalton Trans., 2014, 43, 14257–14264
C(1)–M(1) C(n)–M(1) C(1)–M(1)–C(n) C(1)plane⋯C(n)plane C(1)plane⋯flanking aryl plane
1.939(3) 1.939(3) 175.78(12) 89.07(10) 85.37(10) 78.21(10) 87.21(9) 88.88(10)
2.112(2) 2.112(2) 180 78.33(10) 85.79(5)
2.099(4) 2.099(4) 180 78.46(18) 85.99(7)
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Fig. 2 Crystal structures of [2,6-(2,6-Xyl)2C6H3]2Zn (1; left) and (2,6-Pmp2C6H3)2Hg (9; right) highlighting the linearity in the C–M–C angles for these complexes. Displacement ellipsoids are set at the 50% probability level and hydrogen atoms omitted for clarity. Symmetry operation: ’ = −x + 1/4, −y + 1/4, z.
The C–M–C angles in 2,6-Xyl and Pmp-substituted complexes 1–3 and 7–9 [175.78(12)°–180°] (Fig. 2) are similar to the essentially linear coordination displayed by the zinc diaryl Mes2Zn,7,22 and ( p-CF3C6H4)2Zn23 as well as two-coordinate Mes2Cd and the mercury diaryls Mes2Hg 8 and [2,6Mes2C6H3]2Hg.9 All of the solid state structures of these complexes contain one molecule in the asymmetric unit apart from 8 and 9 (Fig. 2) which contain one quarter of a molecule in the asymmetric unit with the rest being generated by symmetry (symmetry operation = –x + 1/4, −y + 1/4, z), leading to C–M–C angles of 180°. The C–Zn–C angle in the 3,5-Xyl substituted 4 [171.18(15)°] deviates more from linearity than in the 2,6-Xyl and Pmp-substituted diaryls (Fig. 3). A similar deviation has also been observed in the analogous two-coordinate terphenyl (2,6Naph2C6H3)2Zn [168.27(9)°],14 and in the case of 4 this brings ortho-hydrogen atoms on the flanking 3,5-xylyl rings into proximity with the Zn(II) centre [distances H(8)⋯Zn(1) = 2.564 Å, H(16)⋯Zn(1) = 2.874 Å, H(34)⋯Zn(1) = 2.594 Å, H(42)⋯Zn(1) = 2.499 Å; C(8)⋯Zn(1) = 2.8159(13) Å, C(16)⋯Zn(1) = 3.1385(14) Å, C(34)⋯Zn(1) = 2.9250(13) Å, C(42)⋯Zn(1) = 2.9245(13) Å are
within the sum of van der Waals radii for these elements].24,25 This has been attributed to the placement of the methyl groups on the flanking aryl ring being positioned away from the central metal in the complex allowing rotation of the flanking aryl groups. The angles between the least-squares mean planes of the flanking 3,5-xylyl groups and the central aryl ring in 4 lie in the range 40.36(5)–56.11(5)° and are significantly more acute than the analogous values for 1 [80.73(19)– 88.4(2)°] and 7 [78.21(10)–88.88(10)°], presumably for steric reasons. The two metal-substituted aryl rings in these zinc complexes are oriented almost perpendicular to each other in order to reduce steric strain, with the torsion angle between the planes of the two metal-substituted aryl rings varying between 83.6(2)° (for 1) and 89.07(10)° (for 7). The 3,5-xylyl-substituted 5 and 6 (Fig. 3) show smaller deviations from linearity as opposed to 4 [174.10(9)° for 5 and 176.4(2)° for 6] which is similar to (C6F5)2Cd [173.9(1)°].19b 5 and 6 show a comparable orientation of the flanking aryls to 4 which again results in the ortho-hydrogen atoms on the flanking aryl groups being closer to the central cadmium(II) [H(8)⋯Cd(1) = 2.9259 Å, H(16)⋯Cd(1) = 2.8028 Å, H(34)⋯Cd(1)
Fig. 3 Molecular structures of [2,6-(3,5-Xyl)2C6H3]2Zn (4; left) and [2,6-(3,5-Xyl)2C6H3]2Hg (6; right; showing possible secondary ligand interactions as dashed lines). Displacement ellipsoids are drawn at the 50% probability level. Hydrogen atoms are omitted for clarity.
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= 2.7151 Å, H(42)⋯Cd(1) = 2.5981 Å; C(8)⋯Cd(1) = 3.233(3) Å, C(42)⋯Cd(1) = 3.099(3) Å, C(34)⋯Cd(1) = 3.064(3) Å, C(16)⋯ Cd(1) = 3.067(3) Å] and mercury(II) [H(8)⋯Hg(1) = 2.9668 Å, H(16)⋯Hg(1) = 2.9023 Å, H(34)⋯Hg(1) = 2.6504 Å, H(42)⋯ Hg(1) = 2.7901 Å; C(8)⋯Hg(1) = 3.241(7) Å, C(16)⋯Hg(1) = 3.140(7) Å, C(34)⋯Hg(1) = 3.064(7) Å, C(42)⋯Hg(1) = 3.114(6) Å]. As for 4 these distances are all within the sum of the relevant van der Waals radii (C–Cd = 3.95 Å; C–Hg = 3.92 Å).24 The angles formed between the flanking 3,5-Xyl groups and the central aryl ring in 5 [range 45.00(10)–56.33(9)°] and 6 [range 47.1(2)–57.8(2)°] are broadly similar to those for 4. The torsion angle between the two planes of the central metal substituted aryl rings on each ligand are similar to each other [84.2(3)° (2), 86.62(18)° (3), 86.63(7)° (5), 86.03(19)° (6), 78.33(10)° (8) and 78.46(18)° (9)]; by being approximately perpendicular they reduce the steric interactions between the two ligands.
3. Conclusions Three series of crystallographically characterised two-coordinate Group 12 bis-terphenyl complexes (2,6-Ar2C6H3)2M (M = Zn, Cd, Hg; Ar = 2,6-Xyl 1–3; 3,5-Xyl 4–6; Pmp 7–9), are reported. These are the first homoleptic d-block complexes featuring any of these ligands. Their isolation and characterisation allows the analysis of structural changes produced by relatively subtle differences in ligand properties, particularly sterics, and in this case to a smaller extent, electronics. Complexes 4–6 show narrower C–M–C bond angles and contain secondary ligand interactions that are not seen in the analogous complexes 1–3 and 7–9.
4. 4.1.
Experimental General
All manipulations were carried out under an argon or nitrogen atmosphere using standard Schlenk line or glove box techniques. Hexane, THF and toluene were pre-dried over Na wire prior to passing through a column of 4 Å molecular sieves (hexane) or distilled over Na/benzophenone (THF) or potassium (toluene), followed by storage over a potassium mirror (hexane, toluene) or 4 Å molecular sieves (THF). Lithium complexes [2,6-Ar2C6H3Li]2 (Ar = 2,6-Xyl, 3,5-Xyl, Pmp)16,17 and anhydrous ZnCl2 and CdCl2 were prepared by minor modifications of literature methods.26 HgBr2 was dried in vacuo at room temperature for 24 hours prior to use. Benzene-d6 (Goss) was dried over potassium and degassed with three freeze– pump–thaw cycles prior to use. 1H, 13C{1H}, 113Cd{1H} and 199 Hg{1H} NMR spectra for these complexes were collected on Bruker DPX 400, AV 400 or AV(III) 400 spectrometers. Residual signals of solvent were used as references for 1H and 13C{1H} NMR spectroscopy and chemical shifts are quoted in ppm relative to TMS (1H and 13C{1H}), 0.1 M Cd(ClO4)2–D2O solution (113Cd{1H}) and HgMe2 (199Hg{1H}). Elemental analyses were performed by Mr Stephen Boyer, Microanalysis Service,
14260 | Dalton Trans., 2014, 43, 14257–14264
London Metropolitan University. Mass spectrometry was performed by Dr Mick Cooper at the University of Nottingham and by the EPSRC National Mass Spectrometry Facility, Swansea University. (Caution: Cadmium and mercury compounds are known for their toxicity, and great care must be taken in their manipulation.) 4.2.
Syntheses
4.2.1. Synthesis of [2,6-(2,6-Xyl)2C6H3]2M (M = Zn 1, Cd 2, Hg 3). A mixture of [2,6-(2,6-Xyl)2C6H3Li]2 (200 mg, 0.34 mmol) and MX2 (0.34 mmol, MX2 = ZnCl2, CdCl2, HgBr2) in toluene (50 mL) and THF (5 mL) at −78 °C was allowed to warm slowly to room temperature and stirred for 12 hours. Removal of solvent in vacuo and extraction of the resulting white solid with hexane (20 mL) followed by storage for 24 hours at −30 °C resulted in clear, colourless crystals of 1–3 in isolated yields of 54 mg (25%), 43 mg (19%) and 78 mg (30%), respectively, suitable for X-ray diffraction studies. Data for 1. 1H NMR (C6D6, 400.07 MHz, 298 K): δ ( ppm) = 1.79 (s, 24H, o-CH3 of Xyl), 6.76 (d, 4H, J = 7.5 Hz, m-H of C6H3), 7.02 (m, 12H, m- and p-H of Xyl), 7.11 (t, 2H, J = 7.5 Hz, p-H of C6H3). 13C{1H}NMR (C6D6, 100.63 MHz, 298 K) δ ( ppm) = 22.2 (o-CH3 of Xyl), 125.9 (m-CH of C6H3), 127.6 (m-CH of Xyl), 128.5 ( p-CH of Xyl), 129.3 ( p-CH of C6H3), 136.6 (o-C of Xyl), 146.3 (o-C of C6H3), 150.3 (i-C of Xyl), 152.3 (i-C of C6H3). IR (nujol mull) ν/cm−1 = 1614 (w), 1558 (w), 1261 (m), 1075 (m, br), 1030 (m, br), 804 (m), 768 (m), 741 (m). Elemental analysis C44H42Zn: calcd C 83.07, H 6.65; found C 82.86, H 6.50. EI-MS: m/z (%) = 634.2 (6%) [M]+, 619.2 (2%) [M − Me]+, 350.1 (2%) [(2,6-Xyl)2C6H3Zn]+, 284.2 (100%) [(2,6-Xyl)2C6H3]+, 270.1 (11%) [(2,6-Xyl)2C6H3 − Me]+, 255.1 (14%) [(2,6-Xyl)2C6H3 − 2Me]+, 240.1 (4%) [(2,6-Xyl)2C6H3 − 3Me]+. Data for 2. 1H NMR (C6D6, 400.07 MHz, 298 K): δ ( ppm) = 1.80 (s, 24H, o-CH3), 6.87 (d, 4H, J = 7.6 Hz, m-H of C6H3), 7.01 (m, 12H, m- and p-H of Xyl), 7.14 (t, 2H, J = 7.5 Hz, p-H of C6H3). 13C{1H} NMR (C6D6, 100.63 MHz, 298 K) δ ( ppm) = 21.2 (o-CH3 of Xyl), 124.9 (m-CH of C6H3), 126.9 (m-CH of Xyl), 127.8 ( p-CH of Xyl), 128.1 ( p-CH of C6H3), 135.7 (o-C of Xyl), 146.6 (o-C of C6H3), 149.4 (i-C of Xyl), 161.6 (i-C of C6H3). 113Cd{1H} NMR (C6D6, 88.77 MHz, 298 K): δ ( ppm) = 403.52. IR (nujol mull) ν/cm−1 = 1614 (w), 1261 (m), 1096 (w, br), 1029 (m, br), 802 (m, br), 768 (w), 739 (w). Elemental analysis C44H42Cd: calcd C 77.35, H 6.20; found C 77.26, H 6.29. EI-MS: m/z (%) = 684.3 (20%) [M]+, 669.3 (4%) [M − Me]+, 399.1 (5%) [(2,6-Xyl)2C6H3Cd]+, 284.0 (100%) [(2,6-Xyl)2C6H3]+ 270.0 (25%) [(2,6-Xyl)2C6H3 − Me]+, 255.0 (15%) [(2,6-Xyl)2C6H3 − 2Me]+. Data for 3. 1H NMR (C6D6, 400.07 MHz, 298 K): δ ( ppm) = 1.78 (s, 24H, o-CH3), 6.92 (d, 4H, J = 7.5 Hz, m-H of C6H3), 7.04 (m, 14H, p-H of C6H3 and m- and p-H of Xyl). 13C{1H} NMR (C6D6, 100.63 MHz, 298 K) δ ( ppm) = 21.8 (o-CH3 of Xyl), 127.2 (m-CH of C6H3), 127.6 (m-CH of Xyl), 128.1 ( p-CH of Xyl), 128.7 ( p-CH of C6H3), 136.7 (o-C of Xyl), 145.2 (o-C of C6H3), 149.0 (i-C of Xyl), 172.4 (i-C of C6H3). 199Hg{1H} NMR (C6D6, 71.67 MHz, 298 K) δ ( ppm) = −679.77. IR (nujol mull) ν/cm−1 = 2732 (w), 1924 (w), 1852 (w), 1614 (w), 1579 (w), 1562 (w), 1260 (m), 1161 (m), 1077 (m, br), 1030 (m, br), 803 (m), 767 (s), 743 (m). Elemental
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analysis C44H42Hg: calcd C 68.51, H 5.49; found C 68.39, H 5.54. EI-MS: m/z (%) = 772.3 (3%) [M]+, 284.2 (100%) [(2,6-Xyl)2C6H3]+, 270.1 (16%) [(2,6-Xyl)2C6H3 − Me]+, 255.1 (15%) [(2,6-Xyl)2C6H3 − 2Me]+, 240.1 (4%) [(2,6Xyl)2C6H3 − 3Me]+. 4.2.2. Synthesis of [2,6-(3,5-Xyl)2C6H3]2M (M = Zn 4, Cd 5, Hg 6). A mixture of [2,6-(3,5-Xyl)2C6H3Li]2 (200 mg, 0.34 mmol) and MX2 (0.34 mmol, MX2 = ZnCl2, CdCl2, HgBr2) in toluene (50 mL) and THF (5 mL) at −78 °C were allowed to warm slowly to room temperature and stirred for 12 hours. Removal of solvent in vacuo and extraction of the resulting white solid with hexane (20 mL) followed by storage for 24 hours at −30 °C resulted in clear colourless crystals of 4–6 in isolated yields of 90 mg (41%), 154 mg (67%) and 30 mg (11%), respectively, suitable for study by X-ray diffraction. Data for 4. 1H NMR (C6D6, 400.07 MHz, 298 K): δ ( ppm) = 2.04 (s, 24H, m-CH3), 6.62 (s, 4H, p-H of Xyl), 6.97 (s, 8H, o-H of Xyl), 7.11 (t, 2H, J = 7.5 Hz, p-H of C6H3), 7.50 (d, 4H, J = 7.5 Hz, m-H of C6H3). 13C{1H} NMR (C6D6, 100.63 MHz, 298 K) δ ( ppm) = 21.1 (m-CH3 of Xyl), 125.0 (m-CH of C6H3), 125.5 (o-CH of Xyl), 128.3 ( p-CH of C6H3), 128.7 ( p-CH of Xyl), 138.8 (m-C of Xyl), 148.1 (o-C of C6H3), 150.9 (i-C of Xyl), 153.6 (i-C of C6H3). IR (nujol mull) ν/cm−1 = 2957 (s), 1959 (w), 1630 (m), 1599 (w), 1261 (s), 1096 (s, br), 1020 (s, br), 799 (s, br), 671 (m). Elemental analysis C44H42Zn: calcd C 83.07, H 6.65; found C 82.86, H 6.44. EI-MS: m/z (%) = 634.3 (35%) [M]+, 349.1 (9%) [(3,5-Xyl)2C6H3Zn]+, 284.2 (22%) [(3,5-Xyl)2C6H3]+, 270.1 (18%) [(3,5-Xyl)2C6H3 − Me]+, 255.1 (17%) [(3,5-Xyl)2C6H3 − 2Me]+, 240.1 (11%) [(3,5-Xyl)2C6H3 − 3Me]+. Data for 5. 1H NMR (C6D6, 400.07 MHz, 298 K): δ ( ppm) = 2.07 (s, 24H, m-CH3), 6.65 (s, 4H, p-H of Xyl), 7.03 (s, 8H, o-H of Xyl), 7.28 (t, 2H, J = 7.4 Hz, p-H of C6H3), 7.51 (d, 4H, J = 7.4 Hz, m-H of C6H3). 13 C{1H} NMR (C6D6, 100.63 MHz, 298 K) δ ( ppm) = 21.7 (m-CH3 of Xyl), 126.1 ( p-CH of C6H3), 126.3 (o-CH of Xyl), 128.3 (m-CH of C6H3), 129.2 ( p-CH of Xyl), 139.1 (m-C of Xyl), 149.8 (o-C of C6H3), 151.4 (i-C of Xyl), 161.0 (i-C of C6H3). 113 Cd{1H} NMR (C6D6, 88.77 MHz, 298 K): δ ( ppm) = 466.08. IR (nujol mull) ν/cm−1 = 2362 (w), 2342 (w), 1703 (w), 1599 (s), 1558 (m), 1260 (s), 796 (s). Elemental analysis C44H42Cd: calcd C 77.35, H 6.20; found C 77.23, H 6.13. EI-MS: m/z (%) = 684.3 (27%) [M]+, 399.1 (16%) [(3,5-Xyl)2C6H3Cd]+, 285.2 (49%) [(3,5Xyl)2C6H3]+, 270.1 (45%) [(3,5-Xyl)2C6H3 − Me]+, 255.1 (37%) [(3,5-Xyl)2C6H3 − 2Me]+, 239.1 (31%) [(3,5-Xyl)2C6H3 − 3Me]+. Data for 6. 1H NMR (C6D6, 400.07 MHz, 298 K): δ ( ppm) = 2.12 (s, 24H, CH3), 6.68 (s, 4H, p-H of Xyl), 7.07 (s, 8H, o-H of Xyl), 7.19 (t, 2H, J = 7.6 Hz, p-H of C6H3), 7.49 (d, 4H, J = 7.5 Hz, m-H of C6H3). 13C{1H} NMR (C6D6, 100.63 MHz, 298 K) δ ( ppm) = 21.8 (m-CH3 of Xyl), 126.8 (o-CH of Xyl), 127.7 ( p-CH of C6H3), 127.8 (m-CH of C6H3), 129.2 ( p-CH of Xyl), 138.0 (m-C of Xyl), 147.0 (o-C of C6H3), 150.4 (i-C of Xyl), 167.8 (i-C of C6H3). 199Hg{1H} NMR (C6D6, 71.67 MHz, 298 K) δ ( ppm) = −564.31. IR (nujol mull) ν/cm−1 = 2361 (w), 2341 (w), 1560 (w), 1261 (m), 1095 (m, br), 1022 (m, br), 853 (w), 797 (m). Elemental analysis C44H42Hg: calcd C 68.51, H 5.49; found C 68.60, H 5.52. EI-MS: m/z (%) = 772.3 (15%) [M]+, 487.1 (5%) [(3,5Xyl)2C6H3Hg]+, 285.2 (65%) [(3,5-Xyl)2C6H3]+, 270.1 (43%) [(3,5-
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Xyl)2C6H3 − Me]+, 255.1 (37%) [(3,5-Xyl)2C6H3 − 2Me]+, 239.1 (35%) [(3,5-Xyl)2C6H3 − 3Me]+. 4.2.3. Synthesis of [2,6-(2,6-Pmp)2C6H3]2M (M = Zn 7, Cd 8, Hg, 9). A solution of [2,6-Pmp2C6H3Li]2 (200 mg, 0.27 mmol) in toluene (30 mL) was added dropwise to a solution of MX2 (0.27 mmol, MX2 = ZnCl2, CdCl2, HgBr2) in a mixture of toluene (30 mL) and THF (3 mL) at −78 °C. The mixture was allowed to warm slowly to room temperature overnight with stirring. The solvent was removed in vacuo and the resulting solid was extracted into hexane (10 mL). Data for 7. The volume of the solution of 7 in hexane was reduced by half in vacuo, followed by storage at room temperature overnight, resulting in colourless crystals of 7·0.5C6H14 (100 mg, 24%). The crystals were dried in vacuo and analysed as 7. 1H NMR (C6D6, 400.07 MHz, 298 K): δ ( ppm) = 1.94 (s, 24H, o-CH3 of Pmp), 2.29 (s, 12H, p-CH3 of Pmp), 2.40 (s, 24H, m-CH3 of Pmp), 6.95 (d, 4H, J = 7.6 Hz, m-H of C6H3), 7.29 (m, 2H, p-H of C6H3). 13C{1H} NMR (C6D6, 100.63 MHz, 298 K) δ ( ppm) = 17.2 ( p-CH3 of Pmp), 17.7 (m-CH3 of Pmp), 18.4 (o-CH3 of Pmp), 126.6 (m-CH of C6H3), 129.0 ( p-CH of C6H3), 132.0 (quaternary-C of Pmp), 132.1 (quaternary-C of Pmp), 134.2 (quaternary-C of Pmp), 144.6 (o-C of C6H3), 152.6 (i-C of Pmp), 153.2 (i-C of C6H3). IR (nujol mull) ν/cm−1 = 3548 (w), 3456 (w), 2957 (s), 1614 (w), 1558 (w), 1261 (m), 1096 (m, br), 1025 (m, br), 803 (m, br), 736(w). Elemental analysis C56H66Zn: calcd C 83.60, H 8.27; found C 83.42, H 8.17. EI-MS: m/z (%) = 802.6 (15%) [M]+, 787.6 (5%) [M − Me]+, 433.2 (0.5%) [Pmp2C6H3Zn]+, 368.2 (100%) [Pmp2C6H3]+, 353.2 (20%) [Pmp2C6H3 − Me]+, 339.2 (12%) [Pmp2C6H3 − 2Me]+, 323.1 (8%) [Pmp2C6H3 − 3Me]+, 309.1 (5%) [Pmp2C6H3 − 4Me]+, 294.1 (1%) [Pmp2C6H3 − 5Me]+. Data for 8. Storage of 8 in hexane at 6 °C overnight resulted in colourless crystals of pure product (38 mg, 16%). 1H NMR (C6D6, 400.07 MHz, 298 K): δ (ppm) = 1.82 (s, 24H, o-CH3 of Pmp), 2.17 (s, 12H, p-CH3 of Pmp), 2.26 (s, 24H, m-CH3 of Pmp), 6.94 (d, 4H, J = 7.2 Hz, m-H of C6H3), 7.18 (m, 2H, p-H of C6H3). 13C{1H} NMR (C6D6, 100.63 MHz, 298 K): δ (ppm) = 16.5 (p-CH3), 17.1 (m-CH3), 17.8 (o-CH3), 125.7 (m-CH of C6H3), 127.9 (p-CH of C6H3), 131.1 (quaternary-C of Pmp), 131.7 (quaternary-C of Pmp), 133.5 (quaternary-C of Pmp), 144.5 (o-C of C6H3), 151.6 (i-C of Pmp), 162.5 (i-C of C6H3). 113Cd{1H} NMR (C6D6, 88.77 MHz, 298 K): δ (ppm) = 393.47. IR (nujol mull) ν/cm−1 = 2728 (w), 1614 (w), 1563 (w), 1261 (w), 1246 (w), 1155 (w) 1100(m, br), 1061 (m, br), 1030 (m, br) 966 (w), 838 (w, br), 803 (w, br), 788 (m), 740 (m), 658 (w). Elemental analysis C56H66Cd: calcd C 78.99, H 7.81; found C 78.71, H 7.62. EI-MS: 837.4 (2.5%) [M − Me]+, 483.2 (7.2%) [Pmp2(C6H3)Cd]+, 368.2 (100%) [Pmp2(C6H2)]+. Data for 9. The solution of 9 in hexane was reduced in vacuo by half, followed by storage at room temperature overnight, resulting in colourless crystals of pure product (88 mg, 36%). 1H NMR (C6D6, 400.07 MHz, 298 K): δ (ppm) = 1.61 (s, 24H, o-CH3 of Pmp), 2.26 (s, 12H, p-CH3 of Pmp), 2.32 (s, 24H, m-CH3 of Pmp), 6.88 (d, 4H, J = 7.5 Hz, m-H of C6H3), 7.13 (t, 2H, J = 7.4 Hz, p-H of C6H3). 13C{1H} NMR (C6D6, 100.63 MHz, 298 K): δ (ppm) = 16.6 (p-CH3 of Pmp), 17.1 (m-CH3 of Pmp), 17.7 (o-CH3 of Pmp), 127.4 (m-CH of C6H3), 127.7 (p-CH of C6H3), 128.1 (quaternary-C
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Table 4 Crystallographic data for compounds 1–9
Formula Mw Crystal system Space group Crystal size/mm a (Å) b (Å) c (Å) α (°) β (°) γ (°) V (Å3) Z T (K) Dcalc (g cm−3) F000 μ (mm–1) θ range for data collection (°) Max. and min. transmission Reflns measd Independent reflns Rint Final GooF R1, wR2 [I > 2σ(I)] R1, wR2 (all data) Min. and max. electron densities (e Å−3)
Formula Mw Crystal system Space group Crystal size/mm a (Å) b (Å) c (Å) α (°) β (°) γ (°) V (Å3) Z T (K) Dcalc (g cm−3) F000 μ (mm–1) θ range for data collection (°) Max. and min. transmission Reflns measd Independent reflns Rint Final GooF R1, wR2 [I > 2σ(I)] R1, wR2 (all data) Min. and max. electron densities (e Å–3)
1
2
3
4
5
C44H42Zn 636.15 Tetragonal P41 0.24 × 0.20 × 0.09 10.4016(7) 10.4016(7) 31.197(4) 90 90 90 3375.3(6) 4 90(2) 1.252 1344 0.758 1.96–27.49 0.822 and 0.721 21 418 7624 0.0544 1.18 0.0551, 0.105 0.0612, 0.109 –0.37, 0.60
C44H42Cd 683.18 Tetragonal P41 0.14 × 0.12 × 0.11 10.5072(3) 10.5072(3) 31.0528(17) 90 90 90 3428.3(2) 4 90(2) 1.324 1416 0.666 2.05–27.51 0.746 and 0.647 42 410 7863 0.0891 1.15 0.0486, 0.0884 0.0547, 0.0906 –0.50, 0.81
C44H42Hg 771.37 Tetragonal I41/a 0.17 × 0.14 × 0.11 20.903(9) 20.903(9) 31.72(3) 90 90 90 13 861(14) 16 90(2) 1.479 6176 4.471 1.88–27.53 0.430 and 0.320 60 540 7895 0.107 1.06 0.0427, 0.0775 0.0734, 0.0856 –0.47, 1.41
C44H42Zn 636.15 Triclinic ˉ P1 0.15 × 0.10 × 0.07 10.6431(7) 11.2772(6) 15.6417(7) 81.846(4) 87.869(4) 65.639(6) 1692.47(16) 2 120(2) 1.248 672 1.214 4.35–74.65 1.007 and 0.938 24 405 6784 0.0206 1.03 0.0275, 0.0716 0.0302, 0.0736 –0.26, 0.30
C44H42Cd 683.18 Triclinic ˉ P1 0.85 × 0.47 × 0.46 10.748(3) 12.914(4) 13.331(4) 76.688(4) 83.692(4) 78.257(4) 1759.1(9) 2 90(2) 1.29 708 0.649 1.94–25.03 0.746 and 0.598 11 908 6047 0.0230 1.06 0.0280, 0.0678 0.0350, 0.0702 –0.55, 0.50
6
7·0.5C6H14
8
9
C44H42Hg 771.37 Triclinic ˉ P1 0.25 × 0.25 × 0.07 10.688(2) 12.974(3) 13.401(3) 76.323(3) 83.448(3) 78.253(3) 1763.5(6) 2 120(2) 1.453 772 4.393 2.01–27.55 0.43 and 0.311 15 701 7950 0.0538 0.98 0.0528, 0.0969 0.0821, 0.1062 −0.87, 1.75
C59H73Zn 847.54 Monoclinic P21/n 0.16 × 0.05 × 0.04 12.178(3) 22.671(5) 18.854(4) 90 94.559(4) 90 5189(2) 4 90(2) 1.085 1828 0.508 2.10–25.50 0.746 and 0.572 27 280 9593 0.0521 1.08 0.0566, 0.1335 0.0744, 0.1402 −0.41, 0.67
C56H66Cd 851.49 Orthorhombic Fddd 0.16 × 0.13 × 0.10 13.978(5) 18.737(7) 34.854(12) 90 90 90 9129(5) 8 90(2) 1.239 3600 0.514 2.34–27.50 0.746 and 0.676 13 736 2628 0.0305 1.09 0.0275, 0.0713 0.0295, 0.0733 −0.31, 0.94
C56H66Hg 939.68 Orthorhombic Fddd 0.11 × 0.10 × 0.05 13.998(3) 18.670(4) 34.919(8) 90 90 90 9126(3) 8 90(2) 1.368 3856 3.409 1.91–27.57 0.43 and 0.324 13 405 2653 0.0471 1.05 0.0254, 0.0619 0.0313, 0.0648 −0.81, 1.38
of Pmp), 131.4 (quaternary-C of Pmp), 133.5 (quaternary-C of Pmp), 142.7 (o-C of C6H3), 150.7 (i-C of Pmp), 173.0 (i-C of C6H3). 199Hg{1H} NMR (C6D6, 71.67 MHz, 298 K) δ (ppm) −702.88. IR (nujol mull) ν/cm−1 = 2727 (w), 1614 (w), 1569 (w), 1305 (w, br), 1261 (w), 1155 (w, br), 1104 (m, br), 1061 (m, br), 1032 (m, br), 966 (w), 838 (w), 804 (w), 788 (m), 743 (m), 657 (w). Elemental analysis C56H66Hg: calcd C 71.57, H 7.08; found C 71.86, H 7.13. EI-MS: m/z (%) = 940.6 (0.3%) [M]+, 369.3 [2,6Pmp2C6H3]+ (31.9%), 368.3 (100%) [2,6-Pmp2C6H2]+.
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Crystallography
Crystals of 1–9 were mounted on MicroMounts™ (Mitegen) using YR-1800 perfluoropolyether oil (Lancaster) and cooled rapidly in a stream of cold nitrogen using an Oxford Cryosystems low-temperature device.27 Diffraction data for 1–3 and 5–9 (90 K) were acquired on a Bruker SMART APEX or a Bruker SMART1000 diffractometer, equipped with graphite-monochromated Mo-Kα radiation sources (λ = 0.71073 Å), and for 4
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(120 K) on an Agilent SuperNova CCD area detector diffractometer equipped with a mirror-monochromated Cu-Kα radiation source (λ = 1.54184 Å). Intensities were integrated from data recorded on 0.3° (APEX and SMART1000) or 1° (SuperNova) frames by ω rotation. Semi-empirical absorption corrections based on symmetry-equivalent and repeat reflections (APEX and SMART1000) or Gaussian grid face-indexed absorption corrections with a beam profile correction (SuperNova) were applied. All non-H atoms were located using direct methods and difference Fourier syntheses. All non-H atoms were refined with anisotropic displacement parameters. Hydrogen atoms were constrained in calculated positions and refined with a riding model. Programs used were CrysAlisPro28 and Bruker AXS SMART29 (control), CrysAlisPro28 and Bruker AXS SAINT29 (integration), and SHELXS,30 SHELXL30 and OLEX231 (structure solution, structure refinement and molecular graphics). In the crystal structure of 1 a second twin component was detected: the twin law was (−1 0 0 / 0 1 0 / 0 0 −1) and the twin fraction refined to 0.336(14). Merohedral crystal twinning [twin law (0 1 0 / 1 0 0 / 0 0 −1)] was detected for 2 and the twin fraction refined to 0.3834(13). The hexane solvent molecule in 7·0.5C6H14 was extensively disordered: because this could not be modelled sensibly using alternative atomic sites, PLATON SQUEEZE32 was used to remove the contribution of the disordered solvent to the diffraction data and allow refinement against the “solvent-free” dataset (Table 4).
Acknowledgements We acknowledge the EPSRC and the University of Nottingham for financial support of this research. We also thank Mr Stephen Boyer (Microanalysis Service, London Metropolitan University) for elemental analyses and the Mass Spectrometry Service at the University of Nottingham and EPSRC National Mass Spectrometry Facility, Swansea University for mass spectrometry.
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Ligand influences on homoleptic Group 12 m-terphenyl complexes† Toby J. Blundell, Fiona R. Hastings, Benjamin M. Gridley, Graeme J. Moxey,‡ William Lewis, Alexander J. Blake and Deborah L. Kays* Three m-terphenyl ligands 2,6-Ar2C6H3− [Ar = 2,6-Me2C6H3 (2,6-Xyl); 3,5-Me2C6H3 (3,5-Xyl); 2,3,4,5,6Me5C6 (Pmp)] have been used to stabilise three series of two-coordinate Group 12 diaryl complexes; (2,6Ar2C6H3)2M [M = Zn, Cd, Hg, Ar = 2,6-Xyl 1–3, 3,5-Xyl 4–6, Pmp 7–9], where differing steric demands on the metal centres are imparted. These are the first homoleptic d-block complexes featuring any of these
Received 3rd March 2014, Accepted 3rd April 2014
ligands. Complexes 1–9 have been characterised in solution and the solid state; the analysis of structural
DOI: 10.1039/c4dt00647j
changes produced by differences in ligand properties is reported. In particular, complexes 4–6 show smaller C–M–C bond angles and contain secondary ligand interactions that are not seen in the analogous
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complexes 1–3 and 7–9.
1.
Introduction
Since the first report of diethylzinc by Edward Frankland in 1848,1 the investigation of the synthesis and reactivity of organogroup 12 complexes has become an important research area, driven by the use of these compounds in catalysis and materials chemistry. Examples of this include the key role which organozinc reagents play in a range of fundamental organic transformations,2 copolymerisation reactions between carbon dioxide and epoxides to yield polycarbonate compounds,3 alkali-metal mediated zincation reactions,4 cadmium complexes as molecular precursors for photoluminescent quantum dot synthesis5 and mercury compounds as ligand transmetallation reagents.6 The number of two-coordinate Group 12 organometallic complexes in the literature is relatively low, as solid state structures often contain secondary interactions which result in a metal coordination number of greater than two.7,8 Due to this, more sterically demanding ligands have been utilised to stabilise lower coordination numbers, for example in the m-terphenyl complex (2,6-Mes2C6H3)2Hg (Mes = 2,4,6-Me3C6H2).9 The use of sterically demanding m-terphenyl ligands in Group 12
School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD, UK. E-mail: [email protected]; Fax: +44 (0)115 9513555; Tel: +44 (0)115 9513461 † Electronic supplementary information (ESI) available: Crystallographic data for complexes 1–9, molecular structures and crystallographic data for iodides 2,6Ar2C6H3I (Ar = 2,6-Xyl, 3,5-Xyl, Pmp) and [2,6-(3,5-Xyl)2C6H3Li]2. CCDC 989599–989611. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4dt00647j ‡ Current address: Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia.
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chemistry has led to the synthesis and structural characterisation of the first series to feature homologous Group 12 M–M bonds (2,6-Dipp2C6H3)2M2 (M = Zn, Cd, Hg; Dipp = 2,6-iPr2C6H3), the hydride compounds [(2,6-Dipp2C6H3)MH]n (M = Zn, Cd, n = 2; M = Hg, n = 1)10,11 and (η5-C5H5)2Zr (ZnC6H3-2,6-Trip2)2 (Trip = 2,4,6-iPr3C6H2), which contains a Zn–M–Zn (M = transition metal) moiety.12 Our previous investigations have shown that changes in m-terphenyl ligand architectures can result in significant differences in structure, bonding and small molecule reactivity.13–15 We are interested in deducing how subtle changes in the steric pocket offered by the m-terphenyl ligands can affect the coordination environment around the metal centre, with the eventual aim of tailoring the ligand sterics towards the investigation of bonding and small molecule reactivity. To this end we report three series of two-coordinate Group 12 bis-terphenyls of the form (2,6-Ar2C6H3)2M (M = Zn, Cd, Hg; Ar = 2,6-Xyl, 3,5-Xyl, Pmp), which represent the first series of structurally authenticated homoleptic Group 12 bis-terphenyl complexes. Comparison of the crystal structures of these compounds as a function of flanking aryl group illustrates how the manipulation of the steric pocket provided by these ligands influences the structures of the complexes. The general structures of the ligands used in this investigation are shown in Fig. 1.
Fig. 1 The m-terphenyls used in this investigation: R1 = Me, R2 = R3 = H (2,6-Xyl); R1 = R3 = H, R2 = Me (3,5-Xyl); R1 = R2 = R3 = Me (Pmp).
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2. Results and discussion
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2.1.
Synthesis and spectroscopic characterisation
The reaction between the three lithium complexes [2,6Ar2C6H3Li]2 (Ar = 2,6-Xyl; 3,5-Xyl; Pmp)16,17 and ZnCl2, CdCl2 or HgBr2 in a mixture of toluene and THF at room temperature yields the diaryl complexes [2,6-(2,6-Xyl)2C6H3]2M (M = Zn 1, Cd 2, Hg 3), [2,6-(3,5-Xyl)2C6H3]2M (M = Zn 4, Cd 5, Hg 6) and [2,6-Pmp2C6H3]2M (M = Zn 7, Cd 8, Hg 9), respectively, in low to moderate yields according to Scheme 1, although it must be stressed that these are yields of crystalline materials and are not optimised. Crystallisation of 1–6 was achieved by slow cooling to −30 °C of hexane solutions of the complexes. Crystals of 7·0.5C6H14 and 9 were obtained by storage of saturated hexane solutions at room temperature, whereas slow cooling to 6 °C of a saturated hexane solution of 8 proved successful for crystal growth. Complexes 1–9 have been characterised by NMR spectroscopy, elemental analysis and mass spectrometry, and from the results of single crystal X-ray structure determinations. The NMR spectroscopic measurements on 1–9 all indicate one ligand environment in solution. This is in contrast to the NMR spectra recorded for (2,6-Naph2C6H3)2Zn and (2,6Naph2C6H3)2M(OEt2) (M = Cd, Hg; Naph = 1-C10H7), where syn and anti ligand conformations lead to multiple isomers of the complexes in solution.14 The cadmium and mercury NMR spectra for 2, 3, 5, 6, 8 and 9 each shows a single peak (113Cd{1H} range = 393.47 to 466.08 ppm and 199Hg{1H} range = −546.31 to −702.88 ppm) and are in the ranges observed for similar diaryl compounds.14,18 In both the 113Cd{1H} and 199 Hg{1H} NMR spectra of these complexes the chemical shifts follow a broad upfield trend with increasing steric demands on the metals: [2,6-(3,5-Xyl)2C6H3]2M > [2,6-(2,6-Xyl)2C6H3]2M > [2,6-Pmp2C6H3]2M. 2.2.
Crystallographic characterisation
Apart from the solid state structure of 7·0.5C6H14, which crystallised with half a molecule of hexane in the asymmetric unit, there are no solvent molecules present within the crystal structures of these complexes. As a consequence of the steric demands of the m-terphenyl ligands, complexes 1–9 are monomeric in the solid state. The nearest M⋯M separations are d(Zn⋯Zn) = 9.7 Å (for 4), d(Cd⋯Cd) = 10.5 Å (for 2) and d(Hg⋯Hg) = 9.9 Å (for 3). The solid state structures of these compounds feature the metal centres bound to two terphenyl ligands and the metal centres are two-coordinate in all cases. This is in contrast to the Group 12 complexes of the 2,6-
Naph2C6H3− ligand where the cadmium and mercury diaryls are three-coordinate [(2,6-Naph2C6H3)2M(OEt2) (M = Cd, Hg)],14 and is presumably due to the overall lower steric demands of the 1-naphthyl moiety compared to the 2,6-Xyl, 3,5-Xyl or Pmp substituents. Relevant bond lengths and angles for 1–3 can be found in Table 1, for 4–6 in Table 2 and for 7–9 in Table 3. The Zn–C distances for 1 [Zn(1)–C(1) = 1.949(4) Å, Zn(1)– C(23) = 1.944(4) Å], 4 [Zn(1)–C(1) = 1.9362(13) Å, Zn(1)–C(23) = 1.9402(13) Å] and 7 [Zn(1)–C(1) and Zn(1)–C(29) = 1.939(3) Å], are similar to each other and to the values for two-coordinate (2,6-Naph2C6H3)2Zn [Zn–C = 1.946(2) and 1.955(2) Å].14 Cd–C bond lengths for 2, 5 and 8 and Hg–C bond lengths for 3, 6 and 9 also occur in relatively narrow ranges [Cd–C = 2.112(2)– 2.130(2) Å and Hg–C = 2.087(5)–2.102(6) Å] and are similar to those found for other two-coordinate cadmium8,19 and mercury diaryls.9,20 The shorter M–C distance in the mercury diaryls compared to their cadmium analogues is attributed to the smaller covalent radius of mercury compared to cadmium, and is presumably due to a combination of relativistic effects and the lanthanide contraction.10,21 Table 1
Selected bond lengths (Å) and angles (°) for 1–3
C(1)–M(1) C(23)–M(1) C(1)–M(1)–C(23) C(1)plane⋯C(23)plane C(1)plane⋯flanking aryl plane
Table 2
1 (M = Zn)
2 (M = Cd)
3 (M = Hg)
1.949(4) 1.944(4) 178.7(2) 83.6(2) 88.4(2) 80.73(19) 83.0(2) 84.1(2)
2.115(5) 2.228(5) 179.9(3) 84.2(3) 82.2(3) 87.0(3) 84.3(3) 84.8(3)
2.087(6) 2.101(5) 177.1(2) 86.62(18) 83.34(16) 83.65(16) 83.8(2) 87.4(2)
Selected bond lengths (Å) and angles (°) for 4–6
C(1)–M(1) C(23)–M(1) C(1)–M(1)–C(23) C(1)plane⋯C(23)plane C(1)plane⋯flanking aryl plane
4 (M = Zn)
5 (M = Cd)
6 (M = Hg)
1.9362(13) 1.9402(13) 171.18(5) 86.67(4) 56.11(5) 51.26(5) 50.04(5) 40.36(5)
2.119(2) 2.130(2) 174.10(9) 86.63(7) 52.71(9) 56.33(9) 45.00(10) 48.69(10)
2.093(6) 2.102(6) 176.4(2) 86.03(19) 55.6(2) 57.8(2) 49.6(2) 47.1(2)
Table 3 Selected bond lengths (Å) and angles (°) for 7–9. Symmetry operation: ’ = −x + 1/4, −y + 1/4, z
7 (M = Zn) 8 (M = Cd) 9 (M = Hg) C(n) = C(29) C(n) = C(1′) C(n) = C(1′)
Scheme 1 Synthesis of diaryl complexes (2,6-Ar2C6H3)2M (M = Zn, Cd, Hg; Ar = 2,6-Xyl 1–3; 3,5-Xyl 4–6; Pmp 7–9). Reaction conditions: (i) Toluene–THF, −78 °C→RT, 16 h, −2 LiX.
14258 | Dalton Trans., 2014, 43, 14257–14264
C(1)–M(1) C(n)–M(1) C(1)–M(1)–C(n) C(1)plane⋯C(n)plane C(1)plane⋯flanking aryl plane
1.939(3) 1.939(3) 175.78(12) 89.07(10) 85.37(10) 78.21(10) 87.21(9) 88.88(10)
2.112(2) 2.112(2) 180 78.33(10) 85.79(5)
2.099(4) 2.099(4) 180 78.46(18) 85.99(7)
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Fig. 2 Crystal structures of [2,6-(2,6-Xyl)2C6H3]2Zn (1; left) and (2,6-Pmp2C6H3)2Hg (9; right) highlighting the linearity in the C–M–C angles for these complexes. Displacement ellipsoids are set at the 50% probability level and hydrogen atoms omitted for clarity. Symmetry operation: ’ = −x + 1/4, −y + 1/4, z.
The C–M–C angles in 2,6-Xyl and Pmp-substituted complexes 1–3 and 7–9 [175.78(12)°–180°] (Fig. 2) are similar to the essentially linear coordination displayed by the zinc diaryl Mes2Zn,7,22 and ( p-CF3C6H4)2Zn23 as well as two-coordinate Mes2Cd and the mercury diaryls Mes2Hg 8 and [2,6Mes2C6H3]2Hg.9 All of the solid state structures of these complexes contain one molecule in the asymmetric unit apart from 8 and 9 (Fig. 2) which contain one quarter of a molecule in the asymmetric unit with the rest being generated by symmetry (symmetry operation = –x + 1/4, −y + 1/4, z), leading to C–M–C angles of 180°. The C–Zn–C angle in the 3,5-Xyl substituted 4 [171.18(15)°] deviates more from linearity than in the 2,6-Xyl and Pmp-substituted diaryls (Fig. 3). A similar deviation has also been observed in the analogous two-coordinate terphenyl (2,6Naph2C6H3)2Zn [168.27(9)°],14 and in the case of 4 this brings ortho-hydrogen atoms on the flanking 3,5-xylyl rings into proximity with the Zn(II) centre [distances H(8)⋯Zn(1) = 2.564 Å, H(16)⋯Zn(1) = 2.874 Å, H(34)⋯Zn(1) = 2.594 Å, H(42)⋯Zn(1) = 2.499 Å; C(8)⋯Zn(1) = 2.8159(13) Å, C(16)⋯Zn(1) = 3.1385(14) Å, C(34)⋯Zn(1) = 2.9250(13) Å, C(42)⋯Zn(1) = 2.9245(13) Å are
within the sum of van der Waals radii for these elements].24,25 This has been attributed to the placement of the methyl groups on the flanking aryl ring being positioned away from the central metal in the complex allowing rotation of the flanking aryl groups. The angles between the least-squares mean planes of the flanking 3,5-xylyl groups and the central aryl ring in 4 lie in the range 40.36(5)–56.11(5)° and are significantly more acute than the analogous values for 1 [80.73(19)– 88.4(2)°] and 7 [78.21(10)–88.88(10)°], presumably for steric reasons. The two metal-substituted aryl rings in these zinc complexes are oriented almost perpendicular to each other in order to reduce steric strain, with the torsion angle between the planes of the two metal-substituted aryl rings varying between 83.6(2)° (for 1) and 89.07(10)° (for 7). The 3,5-xylyl-substituted 5 and 6 (Fig. 3) show smaller deviations from linearity as opposed to 4 [174.10(9)° for 5 and 176.4(2)° for 6] which is similar to (C6F5)2Cd [173.9(1)°].19b 5 and 6 show a comparable orientation of the flanking aryls to 4 which again results in the ortho-hydrogen atoms on the flanking aryl groups being closer to the central cadmium(II) [H(8)⋯Cd(1) = 2.9259 Å, H(16)⋯Cd(1) = 2.8028 Å, H(34)⋯Cd(1)
Fig. 3 Molecular structures of [2,6-(3,5-Xyl)2C6H3]2Zn (4; left) and [2,6-(3,5-Xyl)2C6H3]2Hg (6; right; showing possible secondary ligand interactions as dashed lines). Displacement ellipsoids are drawn at the 50% probability level. Hydrogen atoms are omitted for clarity.
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= 2.7151 Å, H(42)⋯Cd(1) = 2.5981 Å; C(8)⋯Cd(1) = 3.233(3) Å, C(42)⋯Cd(1) = 3.099(3) Å, C(34)⋯Cd(1) = 3.064(3) Å, C(16)⋯ Cd(1) = 3.067(3) Å] and mercury(II) [H(8)⋯Hg(1) = 2.9668 Å, H(16)⋯Hg(1) = 2.9023 Å, H(34)⋯Hg(1) = 2.6504 Å, H(42)⋯ Hg(1) = 2.7901 Å; C(8)⋯Hg(1) = 3.241(7) Å, C(16)⋯Hg(1) = 3.140(7) Å, C(34)⋯Hg(1) = 3.064(7) Å, C(42)⋯Hg(1) = 3.114(6) Å]. As for 4 these distances are all within the sum of the relevant van der Waals radii (C–Cd = 3.95 Å; C–Hg = 3.92 Å).24 The angles formed between the flanking 3,5-Xyl groups and the central aryl ring in 5 [range 45.00(10)–56.33(9)°] and 6 [range 47.1(2)–57.8(2)°] are broadly similar to those for 4. The torsion angle between the two planes of the central metal substituted aryl rings on each ligand are similar to each other [84.2(3)° (2), 86.62(18)° (3), 86.63(7)° (5), 86.03(19)° (6), 78.33(10)° (8) and 78.46(18)° (9)]; by being approximately perpendicular they reduce the steric interactions between the two ligands.
3. Conclusions Three series of crystallographically characterised two-coordinate Group 12 bis-terphenyl complexes (2,6-Ar2C6H3)2M (M = Zn, Cd, Hg; Ar = 2,6-Xyl 1–3; 3,5-Xyl 4–6; Pmp 7–9), are reported. These are the first homoleptic d-block complexes featuring any of these ligands. Their isolation and characterisation allows the analysis of structural changes produced by relatively subtle differences in ligand properties, particularly sterics, and in this case to a smaller extent, electronics. Complexes 4–6 show narrower C–M–C bond angles and contain secondary ligand interactions that are not seen in the analogous complexes 1–3 and 7–9.
4. 4.1.
Experimental General
All manipulations were carried out under an argon or nitrogen atmosphere using standard Schlenk line or glove box techniques. Hexane, THF and toluene were pre-dried over Na wire prior to passing through a column of 4 Å molecular sieves (hexane) or distilled over Na/benzophenone (THF) or potassium (toluene), followed by storage over a potassium mirror (hexane, toluene) or 4 Å molecular sieves (THF). Lithium complexes [2,6-Ar2C6H3Li]2 (Ar = 2,6-Xyl, 3,5-Xyl, Pmp)16,17 and anhydrous ZnCl2 and CdCl2 were prepared by minor modifications of literature methods.26 HgBr2 was dried in vacuo at room temperature for 24 hours prior to use. Benzene-d6 (Goss) was dried over potassium and degassed with three freeze– pump–thaw cycles prior to use. 1H, 13C{1H}, 113Cd{1H} and 199 Hg{1H} NMR spectra for these complexes were collected on Bruker DPX 400, AV 400 or AV(III) 400 spectrometers. Residual signals of solvent were used as references for 1H and 13C{1H} NMR spectroscopy and chemical shifts are quoted in ppm relative to TMS (1H and 13C{1H}), 0.1 M Cd(ClO4)2–D2O solution (113Cd{1H}) and HgMe2 (199Hg{1H}). Elemental analyses were performed by Mr Stephen Boyer, Microanalysis Service,
14260 | Dalton Trans., 2014, 43, 14257–14264
London Metropolitan University. Mass spectrometry was performed by Dr Mick Cooper at the University of Nottingham and by the EPSRC National Mass Spectrometry Facility, Swansea University. (Caution: Cadmium and mercury compounds are known for their toxicity, and great care must be taken in their manipulation.) 4.2.
Syntheses
4.2.1. Synthesis of [2,6-(2,6-Xyl)2C6H3]2M (M = Zn 1, Cd 2, Hg 3). A mixture of [2,6-(2,6-Xyl)2C6H3Li]2 (200 mg, 0.34 mmol) and MX2 (0.34 mmol, MX2 = ZnCl2, CdCl2, HgBr2) in toluene (50 mL) and THF (5 mL) at −78 °C was allowed to warm slowly to room temperature and stirred for 12 hours. Removal of solvent in vacuo and extraction of the resulting white solid with hexane (20 mL) followed by storage for 24 hours at −30 °C resulted in clear, colourless crystals of 1–3 in isolated yields of 54 mg (25%), 43 mg (19%) and 78 mg (30%), respectively, suitable for X-ray diffraction studies. Data for 1. 1H NMR (C6D6, 400.07 MHz, 298 K): δ ( ppm) = 1.79 (s, 24H, o-CH3 of Xyl), 6.76 (d, 4H, J = 7.5 Hz, m-H of C6H3), 7.02 (m, 12H, m- and p-H of Xyl), 7.11 (t, 2H, J = 7.5 Hz, p-H of C6H3). 13C{1H}NMR (C6D6, 100.63 MHz, 298 K) δ ( ppm) = 22.2 (o-CH3 of Xyl), 125.9 (m-CH of C6H3), 127.6 (m-CH of Xyl), 128.5 ( p-CH of Xyl), 129.3 ( p-CH of C6H3), 136.6 (o-C of Xyl), 146.3 (o-C of C6H3), 150.3 (i-C of Xyl), 152.3 (i-C of C6H3). IR (nujol mull) ν/cm−1 = 1614 (w), 1558 (w), 1261 (m), 1075 (m, br), 1030 (m, br), 804 (m), 768 (m), 741 (m). Elemental analysis C44H42Zn: calcd C 83.07, H 6.65; found C 82.86, H 6.50. EI-MS: m/z (%) = 634.2 (6%) [M]+, 619.2 (2%) [M − Me]+, 350.1 (2%) [(2,6-Xyl)2C6H3Zn]+, 284.2 (100%) [(2,6-Xyl)2C6H3]+, 270.1 (11%) [(2,6-Xyl)2C6H3 − Me]+, 255.1 (14%) [(2,6-Xyl)2C6H3 − 2Me]+, 240.1 (4%) [(2,6-Xyl)2C6H3 − 3Me]+. Data for 2. 1H NMR (C6D6, 400.07 MHz, 298 K): δ ( ppm) = 1.80 (s, 24H, o-CH3), 6.87 (d, 4H, J = 7.6 Hz, m-H of C6H3), 7.01 (m, 12H, m- and p-H of Xyl), 7.14 (t, 2H, J = 7.5 Hz, p-H of C6H3). 13C{1H} NMR (C6D6, 100.63 MHz, 298 K) δ ( ppm) = 21.2 (o-CH3 of Xyl), 124.9 (m-CH of C6H3), 126.9 (m-CH of Xyl), 127.8 ( p-CH of Xyl), 128.1 ( p-CH of C6H3), 135.7 (o-C of Xyl), 146.6 (o-C of C6H3), 149.4 (i-C of Xyl), 161.6 (i-C of C6H3). 113Cd{1H} NMR (C6D6, 88.77 MHz, 298 K): δ ( ppm) = 403.52. IR (nujol mull) ν/cm−1 = 1614 (w), 1261 (m), 1096 (w, br), 1029 (m, br), 802 (m, br), 768 (w), 739 (w). Elemental analysis C44H42Cd: calcd C 77.35, H 6.20; found C 77.26, H 6.29. EI-MS: m/z (%) = 684.3 (20%) [M]+, 669.3 (4%) [M − Me]+, 399.1 (5%) [(2,6-Xyl)2C6H3Cd]+, 284.0 (100%) [(2,6-Xyl)2C6H3]+ 270.0 (25%) [(2,6-Xyl)2C6H3 − Me]+, 255.0 (15%) [(2,6-Xyl)2C6H3 − 2Me]+. Data for 3. 1H NMR (C6D6, 400.07 MHz, 298 K): δ ( ppm) = 1.78 (s, 24H, o-CH3), 6.92 (d, 4H, J = 7.5 Hz, m-H of C6H3), 7.04 (m, 14H, p-H of C6H3 and m- and p-H of Xyl). 13C{1H} NMR (C6D6, 100.63 MHz, 298 K) δ ( ppm) = 21.8 (o-CH3 of Xyl), 127.2 (m-CH of C6H3), 127.6 (m-CH of Xyl), 128.1 ( p-CH of Xyl), 128.7 ( p-CH of C6H3), 136.7 (o-C of Xyl), 145.2 (o-C of C6H3), 149.0 (i-C of Xyl), 172.4 (i-C of C6H3). 199Hg{1H} NMR (C6D6, 71.67 MHz, 298 K) δ ( ppm) = −679.77. IR (nujol mull) ν/cm−1 = 2732 (w), 1924 (w), 1852 (w), 1614 (w), 1579 (w), 1562 (w), 1260 (m), 1161 (m), 1077 (m, br), 1030 (m, br), 803 (m), 767 (s), 743 (m). Elemental
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analysis C44H42Hg: calcd C 68.51, H 5.49; found C 68.39, H 5.54. EI-MS: m/z (%) = 772.3 (3%) [M]+, 284.2 (100%) [(2,6-Xyl)2C6H3]+, 270.1 (16%) [(2,6-Xyl)2C6H3 − Me]+, 255.1 (15%) [(2,6-Xyl)2C6H3 − 2Me]+, 240.1 (4%) [(2,6Xyl)2C6H3 − 3Me]+. 4.2.2. Synthesis of [2,6-(3,5-Xyl)2C6H3]2M (M = Zn 4, Cd 5, Hg 6). A mixture of [2,6-(3,5-Xyl)2C6H3Li]2 (200 mg, 0.34 mmol) and MX2 (0.34 mmol, MX2 = ZnCl2, CdCl2, HgBr2) in toluene (50 mL) and THF (5 mL) at −78 °C were allowed to warm slowly to room temperature and stirred for 12 hours. Removal of solvent in vacuo and extraction of the resulting white solid with hexane (20 mL) followed by storage for 24 hours at −30 °C resulted in clear colourless crystals of 4–6 in isolated yields of 90 mg (41%), 154 mg (67%) and 30 mg (11%), respectively, suitable for study by X-ray diffraction. Data for 4. 1H NMR (C6D6, 400.07 MHz, 298 K): δ ( ppm) = 2.04 (s, 24H, m-CH3), 6.62 (s, 4H, p-H of Xyl), 6.97 (s, 8H, o-H of Xyl), 7.11 (t, 2H, J = 7.5 Hz, p-H of C6H3), 7.50 (d, 4H, J = 7.5 Hz, m-H of C6H3). 13C{1H} NMR (C6D6, 100.63 MHz, 298 K) δ ( ppm) = 21.1 (m-CH3 of Xyl), 125.0 (m-CH of C6H3), 125.5 (o-CH of Xyl), 128.3 ( p-CH of C6H3), 128.7 ( p-CH of Xyl), 138.8 (m-C of Xyl), 148.1 (o-C of C6H3), 150.9 (i-C of Xyl), 153.6 (i-C of C6H3). IR (nujol mull) ν/cm−1 = 2957 (s), 1959 (w), 1630 (m), 1599 (w), 1261 (s), 1096 (s, br), 1020 (s, br), 799 (s, br), 671 (m). Elemental analysis C44H42Zn: calcd C 83.07, H 6.65; found C 82.86, H 6.44. EI-MS: m/z (%) = 634.3 (35%) [M]+, 349.1 (9%) [(3,5-Xyl)2C6H3Zn]+, 284.2 (22%) [(3,5-Xyl)2C6H3]+, 270.1 (18%) [(3,5-Xyl)2C6H3 − Me]+, 255.1 (17%) [(3,5-Xyl)2C6H3 − 2Me]+, 240.1 (11%) [(3,5-Xyl)2C6H3 − 3Me]+. Data for 5. 1H NMR (C6D6, 400.07 MHz, 298 K): δ ( ppm) = 2.07 (s, 24H, m-CH3), 6.65 (s, 4H, p-H of Xyl), 7.03 (s, 8H, o-H of Xyl), 7.28 (t, 2H, J = 7.4 Hz, p-H of C6H3), 7.51 (d, 4H, J = 7.4 Hz, m-H of C6H3). 13 C{1H} NMR (C6D6, 100.63 MHz, 298 K) δ ( ppm) = 21.7 (m-CH3 of Xyl), 126.1 ( p-CH of C6H3), 126.3 (o-CH of Xyl), 128.3 (m-CH of C6H3), 129.2 ( p-CH of Xyl), 139.1 (m-C of Xyl), 149.8 (o-C of C6H3), 151.4 (i-C of Xyl), 161.0 (i-C of C6H3). 113 Cd{1H} NMR (C6D6, 88.77 MHz, 298 K): δ ( ppm) = 466.08. IR (nujol mull) ν/cm−1 = 2362 (w), 2342 (w), 1703 (w), 1599 (s), 1558 (m), 1260 (s), 796 (s). Elemental analysis C44H42Cd: calcd C 77.35, H 6.20; found C 77.23, H 6.13. EI-MS: m/z (%) = 684.3 (27%) [M]+, 399.1 (16%) [(3,5-Xyl)2C6H3Cd]+, 285.2 (49%) [(3,5Xyl)2C6H3]+, 270.1 (45%) [(3,5-Xyl)2C6H3 − Me]+, 255.1 (37%) [(3,5-Xyl)2C6H3 − 2Me]+, 239.1 (31%) [(3,5-Xyl)2C6H3 − 3Me]+. Data for 6. 1H NMR (C6D6, 400.07 MHz, 298 K): δ ( ppm) = 2.12 (s, 24H, CH3), 6.68 (s, 4H, p-H of Xyl), 7.07 (s, 8H, o-H of Xyl), 7.19 (t, 2H, J = 7.6 Hz, p-H of C6H3), 7.49 (d, 4H, J = 7.5 Hz, m-H of C6H3). 13C{1H} NMR (C6D6, 100.63 MHz, 298 K) δ ( ppm) = 21.8 (m-CH3 of Xyl), 126.8 (o-CH of Xyl), 127.7 ( p-CH of C6H3), 127.8 (m-CH of C6H3), 129.2 ( p-CH of Xyl), 138.0 (m-C of Xyl), 147.0 (o-C of C6H3), 150.4 (i-C of Xyl), 167.8 (i-C of C6H3). 199Hg{1H} NMR (C6D6, 71.67 MHz, 298 K) δ ( ppm) = −564.31. IR (nujol mull) ν/cm−1 = 2361 (w), 2341 (w), 1560 (w), 1261 (m), 1095 (m, br), 1022 (m, br), 853 (w), 797 (m). Elemental analysis C44H42Hg: calcd C 68.51, H 5.49; found C 68.60, H 5.52. EI-MS: m/z (%) = 772.3 (15%) [M]+, 487.1 (5%) [(3,5Xyl)2C6H3Hg]+, 285.2 (65%) [(3,5-Xyl)2C6H3]+, 270.1 (43%) [(3,5-
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Xyl)2C6H3 − Me]+, 255.1 (37%) [(3,5-Xyl)2C6H3 − 2Me]+, 239.1 (35%) [(3,5-Xyl)2C6H3 − 3Me]+. 4.2.3. Synthesis of [2,6-(2,6-Pmp)2C6H3]2M (M = Zn 7, Cd 8, Hg, 9). A solution of [2,6-Pmp2C6H3Li]2 (200 mg, 0.27 mmol) in toluene (30 mL) was added dropwise to a solution of MX2 (0.27 mmol, MX2 = ZnCl2, CdCl2, HgBr2) in a mixture of toluene (30 mL) and THF (3 mL) at −78 °C. The mixture was allowed to warm slowly to room temperature overnight with stirring. The solvent was removed in vacuo and the resulting solid was extracted into hexane (10 mL). Data for 7. The volume of the solution of 7 in hexane was reduced by half in vacuo, followed by storage at room temperature overnight, resulting in colourless crystals of 7·0.5C6H14 (100 mg, 24%). The crystals were dried in vacuo and analysed as 7. 1H NMR (C6D6, 400.07 MHz, 298 K): δ ( ppm) = 1.94 (s, 24H, o-CH3 of Pmp), 2.29 (s, 12H, p-CH3 of Pmp), 2.40 (s, 24H, m-CH3 of Pmp), 6.95 (d, 4H, J = 7.6 Hz, m-H of C6H3), 7.29 (m, 2H, p-H of C6H3). 13C{1H} NMR (C6D6, 100.63 MHz, 298 K) δ ( ppm) = 17.2 ( p-CH3 of Pmp), 17.7 (m-CH3 of Pmp), 18.4 (o-CH3 of Pmp), 126.6 (m-CH of C6H3), 129.0 ( p-CH of C6H3), 132.0 (quaternary-C of Pmp), 132.1 (quaternary-C of Pmp), 134.2 (quaternary-C of Pmp), 144.6 (o-C of C6H3), 152.6 (i-C of Pmp), 153.2 (i-C of C6H3). IR (nujol mull) ν/cm−1 = 3548 (w), 3456 (w), 2957 (s), 1614 (w), 1558 (w), 1261 (m), 1096 (m, br), 1025 (m, br), 803 (m, br), 736(w). Elemental analysis C56H66Zn: calcd C 83.60, H 8.27; found C 83.42, H 8.17. EI-MS: m/z (%) = 802.6 (15%) [M]+, 787.6 (5%) [M − Me]+, 433.2 (0.5%) [Pmp2C6H3Zn]+, 368.2 (100%) [Pmp2C6H3]+, 353.2 (20%) [Pmp2C6H3 − Me]+, 339.2 (12%) [Pmp2C6H3 − 2Me]+, 323.1 (8%) [Pmp2C6H3 − 3Me]+, 309.1 (5%) [Pmp2C6H3 − 4Me]+, 294.1 (1%) [Pmp2C6H3 − 5Me]+. Data for 8. Storage of 8 in hexane at 6 °C overnight resulted in colourless crystals of pure product (38 mg, 16%). 1H NMR (C6D6, 400.07 MHz, 298 K): δ (ppm) = 1.82 (s, 24H, o-CH3 of Pmp), 2.17 (s, 12H, p-CH3 of Pmp), 2.26 (s, 24H, m-CH3 of Pmp), 6.94 (d, 4H, J = 7.2 Hz, m-H of C6H3), 7.18 (m, 2H, p-H of C6H3). 13C{1H} NMR (C6D6, 100.63 MHz, 298 K): δ (ppm) = 16.5 (p-CH3), 17.1 (m-CH3), 17.8 (o-CH3), 125.7 (m-CH of C6H3), 127.9 (p-CH of C6H3), 131.1 (quaternary-C of Pmp), 131.7 (quaternary-C of Pmp), 133.5 (quaternary-C of Pmp), 144.5 (o-C of C6H3), 151.6 (i-C of Pmp), 162.5 (i-C of C6H3). 113Cd{1H} NMR (C6D6, 88.77 MHz, 298 K): δ (ppm) = 393.47. IR (nujol mull) ν/cm−1 = 2728 (w), 1614 (w), 1563 (w), 1261 (w), 1246 (w), 1155 (w) 1100(m, br), 1061 (m, br), 1030 (m, br) 966 (w), 838 (w, br), 803 (w, br), 788 (m), 740 (m), 658 (w). Elemental analysis C56H66Cd: calcd C 78.99, H 7.81; found C 78.71, H 7.62. EI-MS: 837.4 (2.5%) [M − Me]+, 483.2 (7.2%) [Pmp2(C6H3)Cd]+, 368.2 (100%) [Pmp2(C6H2)]+. Data for 9. The solution of 9 in hexane was reduced in vacuo by half, followed by storage at room temperature overnight, resulting in colourless crystals of pure product (88 mg, 36%). 1H NMR (C6D6, 400.07 MHz, 298 K): δ (ppm) = 1.61 (s, 24H, o-CH3 of Pmp), 2.26 (s, 12H, p-CH3 of Pmp), 2.32 (s, 24H, m-CH3 of Pmp), 6.88 (d, 4H, J = 7.5 Hz, m-H of C6H3), 7.13 (t, 2H, J = 7.4 Hz, p-H of C6H3). 13C{1H} NMR (C6D6, 100.63 MHz, 298 K): δ (ppm) = 16.6 (p-CH3 of Pmp), 17.1 (m-CH3 of Pmp), 17.7 (o-CH3 of Pmp), 127.4 (m-CH of C6H3), 127.7 (p-CH of C6H3), 128.1 (quaternary-C
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Table 4 Crystallographic data for compounds 1–9
Formula Mw Crystal system Space group Crystal size/mm a (Å) b (Å) c (Å) α (°) β (°) γ (°) V (Å3) Z T (K) Dcalc (g cm−3) F000 μ (mm–1) θ range for data collection (°) Max. and min. transmission Reflns measd Independent reflns Rint Final GooF R1, wR2 [I > 2σ(I)] R1, wR2 (all data) Min. and max. electron densities (e Å−3)
Formula Mw Crystal system Space group Crystal size/mm a (Å) b (Å) c (Å) α (°) β (°) γ (°) V (Å3) Z T (K) Dcalc (g cm−3) F000 μ (mm–1) θ range for data collection (°) Max. and min. transmission Reflns measd Independent reflns Rint Final GooF R1, wR2 [I > 2σ(I)] R1, wR2 (all data) Min. and max. electron densities (e Å–3)
1
2
3
4
5
C44H42Zn 636.15 Tetragonal P41 0.24 × 0.20 × 0.09 10.4016(7) 10.4016(7) 31.197(4) 90 90 90 3375.3(6) 4 90(2) 1.252 1344 0.758 1.96–27.49 0.822 and 0.721 21 418 7624 0.0544 1.18 0.0551, 0.105 0.0612, 0.109 –0.37, 0.60
C44H42Cd 683.18 Tetragonal P41 0.14 × 0.12 × 0.11 10.5072(3) 10.5072(3) 31.0528(17) 90 90 90 3428.3(2) 4 90(2) 1.324 1416 0.666 2.05–27.51 0.746 and 0.647 42 410 7863 0.0891 1.15 0.0486, 0.0884 0.0547, 0.0906 –0.50, 0.81
C44H42Hg 771.37 Tetragonal I41/a 0.17 × 0.14 × 0.11 20.903(9) 20.903(9) 31.72(3) 90 90 90 13 861(14) 16 90(2) 1.479 6176 4.471 1.88–27.53 0.430 and 0.320 60 540 7895 0.107 1.06 0.0427, 0.0775 0.0734, 0.0856 –0.47, 1.41
C44H42Zn 636.15 Triclinic ˉ P1 0.15 × 0.10 × 0.07 10.6431(7) 11.2772(6) 15.6417(7) 81.846(4) 87.869(4) 65.639(6) 1692.47(16) 2 120(2) 1.248 672 1.214 4.35–74.65 1.007 and 0.938 24 405 6784 0.0206 1.03 0.0275, 0.0716 0.0302, 0.0736 –0.26, 0.30
C44H42Cd 683.18 Triclinic ˉ P1 0.85 × 0.47 × 0.46 10.748(3) 12.914(4) 13.331(4) 76.688(4) 83.692(4) 78.257(4) 1759.1(9) 2 90(2) 1.29 708 0.649 1.94–25.03 0.746 and 0.598 11 908 6047 0.0230 1.06 0.0280, 0.0678 0.0350, 0.0702 –0.55, 0.50
6
7·0.5C6H14
8
9
C44H42Hg 771.37 Triclinic ˉ P1 0.25 × 0.25 × 0.07 10.688(2) 12.974(3) 13.401(3) 76.323(3) 83.448(3) 78.253(3) 1763.5(6) 2 120(2) 1.453 772 4.393 2.01–27.55 0.43 and 0.311 15 701 7950 0.0538 0.98 0.0528, 0.0969 0.0821, 0.1062 −0.87, 1.75
C59H73Zn 847.54 Monoclinic P21/n 0.16 × 0.05 × 0.04 12.178(3) 22.671(5) 18.854(4) 90 94.559(4) 90 5189(2) 4 90(2) 1.085 1828 0.508 2.10–25.50 0.746 and 0.572 27 280 9593 0.0521 1.08 0.0566, 0.1335 0.0744, 0.1402 −0.41, 0.67
C56H66Cd 851.49 Orthorhombic Fddd 0.16 × 0.13 × 0.10 13.978(5) 18.737(7) 34.854(12) 90 90 90 9129(5) 8 90(2) 1.239 3600 0.514 2.34–27.50 0.746 and 0.676 13 736 2628 0.0305 1.09 0.0275, 0.0713 0.0295, 0.0733 −0.31, 0.94
C56H66Hg 939.68 Orthorhombic Fddd 0.11 × 0.10 × 0.05 13.998(3) 18.670(4) 34.919(8) 90 90 90 9126(3) 8 90(2) 1.368 3856 3.409 1.91–27.57 0.43 and 0.324 13 405 2653 0.0471 1.05 0.0254, 0.0619 0.0313, 0.0648 −0.81, 1.38
of Pmp), 131.4 (quaternary-C of Pmp), 133.5 (quaternary-C of Pmp), 142.7 (o-C of C6H3), 150.7 (i-C of Pmp), 173.0 (i-C of C6H3). 199Hg{1H} NMR (C6D6, 71.67 MHz, 298 K) δ (ppm) −702.88. IR (nujol mull) ν/cm−1 = 2727 (w), 1614 (w), 1569 (w), 1305 (w, br), 1261 (w), 1155 (w, br), 1104 (m, br), 1061 (m, br), 1032 (m, br), 966 (w), 838 (w), 804 (w), 788 (m), 743 (m), 657 (w). Elemental analysis C56H66Hg: calcd C 71.57, H 7.08; found C 71.86, H 7.13. EI-MS: m/z (%) = 940.6 (0.3%) [M]+, 369.3 [2,6Pmp2C6H3]+ (31.9%), 368.3 (100%) [2,6-Pmp2C6H2]+.
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Crystallography
Crystals of 1–9 were mounted on MicroMounts™ (Mitegen) using YR-1800 perfluoropolyether oil (Lancaster) and cooled rapidly in a stream of cold nitrogen using an Oxford Cryosystems low-temperature device.27 Diffraction data for 1–3 and 5–9 (90 K) were acquired on a Bruker SMART APEX or a Bruker SMART1000 diffractometer, equipped with graphite-monochromated Mo-Kα radiation sources (λ = 0.71073 Å), and for 4
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(120 K) on an Agilent SuperNova CCD area detector diffractometer equipped with a mirror-monochromated Cu-Kα radiation source (λ = 1.54184 Å). Intensities were integrated from data recorded on 0.3° (APEX and SMART1000) or 1° (SuperNova) frames by ω rotation. Semi-empirical absorption corrections based on symmetry-equivalent and repeat reflections (APEX and SMART1000) or Gaussian grid face-indexed absorption corrections with a beam profile correction (SuperNova) were applied. All non-H atoms were located using direct methods and difference Fourier syntheses. All non-H atoms were refined with anisotropic displacement parameters. Hydrogen atoms were constrained in calculated positions and refined with a riding model. Programs used were CrysAlisPro28 and Bruker AXS SMART29 (control), CrysAlisPro28 and Bruker AXS SAINT29 (integration), and SHELXS,30 SHELXL30 and OLEX231 (structure solution, structure refinement and molecular graphics). In the crystal structure of 1 a second twin component was detected: the twin law was (−1 0 0 / 0 1 0 / 0 0 −1) and the twin fraction refined to 0.336(14). Merohedral crystal twinning [twin law (0 1 0 / 1 0 0 / 0 0 −1)] was detected for 2 and the twin fraction refined to 0.3834(13). The hexane solvent molecule in 7·0.5C6H14 was extensively disordered: because this could not be modelled sensibly using alternative atomic sites, PLATON SQUEEZE32 was used to remove the contribution of the disordered solvent to the diffraction data and allow refinement against the “solvent-free” dataset (Table 4).
Acknowledgements We acknowledge the EPSRC and the University of Nottingham for financial support of this research. We also thank Mr Stephen Boyer (Microanalysis Service, London Metropolitan University) for elemental analyses and the Mass Spectrometry Service at the University of Nottingham and EPSRC National Mass Spectrometry Facility, Swansea University for mass spectrometry.
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